This application claims priority to German Patent Application No. 101 03 775.9 filed on Jan. 27, 2001 and assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference.
The present invention is generally related to compressors and their use and is more specifically related to a scroll compressor having two displacement elements and a method for using such a compressor.
The invention relates to a method for compressing a compressible medium, in which at least two displacement elements, each having at least one limiting face extending helically in the cross section, are orbited in relation to each other under formation of at least one chamber, the volume of the chamber being changed by the orbiting movement, performing a cycle with a suction phase, a compression phase and a discharge phase, the chamber being opened and forming a suction chamber during the suction phase. Further, the invention relates to a scroll compressor with at least two displacement elements operating in relation to each other with an orbiting movement, each having at least one limiting face extending helically in the cross section, the displacement elements forming at least one chamber, which, during the orbiting movement by way of a cycle with a suction phase, a compression phase and a discharge phase has a variable volume, the chamber having during the suction phase a suction chamber with at least one suction opening.
A compressor of this kind is known from U.S. Pat. No. 4,781,549. This document shows a scroll compressor with two orbiting displacement elements, each being limited in the cross section, both inside and outside, by a helically extending limiting face. Both displacement elements have a length of approximately 2xcfx80 in the arc measure. Further, an inner profile end portion of the two displacement elements continuously extends its profile thickness. Together, the displacement elements form at least two chambers. Each chamber performs a cycle with a suction phase, a compression phase and a discharge phase. During the suction phase, the chamber has a suction opening, which is closed again at the end of the suction phase. Subsequently, the compression phase of the chambers starts. Shortly after the start of the compression phase, the chambers are united to form one chamber. The circulation length of a complete cycle amounts to approximately 4xcfx80 in the arc measure.
U.S. Pat. No. 4,527,964 shows a scroll compressor, in which a displacement element extends helically over a length of approximately 3xcfx80 in the arc measure and is orbited in relation to a second displacement element. Both displacement elements have limiting faces, which deviate from a regular helical shape. The moving displacement element has a long outer section with a small curvature. Due to the geometry of the displacement elements, a relatively large backflow to the suction side is generated at the end of the suction phase of this scroll compressor.
U.S. Pat. No. 6,099,279 shows a scroll compressor, whose displacement elements have several helical limiting faces. These also cause a relatively large backflow at the end of a suction phase because of their geometry.
EP 0 069 531 shows a scroll compressor with two displacement elements having a length of less than 3xcfx80 in the arc measure. A relatively large backflow is also generated with this invention, as each displacement element has a long, slightly curved outer section.
Also DE 196 03 110 A1 shows a scroll compressor, whose displacement elements have relatively long, slightly curved outer sections.
Further, from, for example, U.S. Pat. Nos. 5,938,417, 5,547,353, 5,836,752, 3,884,599, 5,318,424, DE 42 15 038 and from the article xe2x80x9cDer Scroll von Bockxe2x80x9d (H. Kaiser, Die Kxc3xa4lte und Klimatechnik, Heft June 1993, pages 334 to 342), scroll compressors are known, which all have displacement elements with a length of approximately 3xcfx80 in the arc measure. Further, the displacement elements have slightly curved and regular outer sections.
The extension of the helical limiting faces of the displacement elements of such scroll compressors is substantially based on a production-technical point of view. Due to the geometry of the helical limiting faces, however, a relatively large backflow from the chamber through the suction opening will be generated at the end of a suction phase. Thus, the scroll compressor loses both capacity and efficiency.
Based on the foregoing, it is the general object of the present invention to improve the thermodynamic conditions during compression of a compressible medium.
With a method as mentioned in the introduction, the present invention provides that for the duration of the suction phase, the suction chamber is reduced by a volume limiting element in such a way that at the end of the suction phase the chamber has a volume of at least 90% of a maximum volume occurring during the suction phase.
Besides being influenced by the helical limiting faces of the displacement element, the volume of the chamber is also influenced by the volume-limiting element. Thus, for example, the adaptation of the chamber volume to a predetermined volume function is possible. During the whole suction phase, the chamber volume can be changed in such a way that it has approximately its maximum volume when the suction opening closes. In this way a favourable volume relation is achieved between the maximum chamber volume and the chamber volume at the time when the suction opening closes. Consequently, only a small backflow from the chamber occurs at the end of the suction phase. This results in good thermodynamic conditions and thus higher efficiency, and a high capacity in relation to the overall size of the compressor. Accordingly, a given overall size of the compressor results in a relatively large suction volume and therefore a large mass flow through the compressor.
It is an advantage of the present invention that the volume of the chamber is reduced by the volume-limiting element over a predetermined circulation length from the beginning of the compression phase. The chamber volume is controllable during the compression phase. In this connection, the chamber volume can be adapted to a volume function over the circulation length, which function is particularly suited for the planned operation. This means that at the beginning of the compression phase a heavier reduction of the volume (relative compression) is possible than at the end of the compression phase.
It is advantageous that the reduction of the volume of the chamber by the volume limiting element from the beginning of the compression phase is finished at the latest after a predetermined circulation length of 1xcfx80 in the arc measure. In this way, a smaller reduction of the volume can be achieved, resulting in a slow discharge. The slow discharge of the gas prevents pressure peaks on the pressure side.
It is particularly advantageous that the suction opening is closed before the end of a discharge phase. Thus, it is prevented that at the end of a suction phase effects on the flow conditions in one chamber will have a damaging influence on another chamber. Particularly, a reduction of the gas quantity sucked in through re-expansion of compressed gas is prevented, which would occur, if the suction opening did not close until after the end of the discharge phase. Thus, it is an advantage of the present invention that the displacement elements do not separate at the inner ends, until the suction opening is closed again at the outer end. This is accomplished because at least one of the displacement elements has a profile back, which projects into the suction chamber.
Thus, the profile back forms a volume-limiting element. For this purpose, each displacement element has a section, which is formed independently of a helical shape. By means of this section, the volume of the chamber can be adapted to a predetermined volume function, which is desired for process reasons. In this way, for example, a favourable volume relation between the maximum chamber volume and the chamber volume at the end of the suction phase can be realised. This again results in a smaller backflow during closing of the suction opening. In this way, a higher capacity and efficiency of the scroll compressor can be obtained.
Further, it is another advantage of the present invention that for a predetermined circulation length at the beginning of the compression phase, the profile back projects into the chamber. In this way, the progress of the compression phase can also be influenced through the embodiment of the profile back. This means that during the compression phase a predetermined change of the chamber volume can be set. For example, it is possible to generate a larger volume reduction at the beginning of the compression phase than at the end of the compression phase. This can reduce the compression phase, which leads to reduced leakage losses between the displacement elements.
It is favourable that the predetermined circulation length from the beginning of the compression phase amounts to a maximum of 1xcfx80 in the arc measure. In this way, a smaller volume reduction and a slow discharge of the compressed gas at the end of the compression phase can be achieved.
It is still another advantage of the present invention that the profile back can rest on an outer profile end portion, which is adapted to the shape of the profile back. This cooperation during a bearing phase of the profile back with a counter piece adapted to it ensures a stable contact between the two displacement elements concerned. Further, this ensures regular flow conditions inside the chamber.
Further, it is favourable that the outer profile end portion has three sections, of which a second section, seen from an outer end, has a larger curvature than a first and a third section. In this connection, the slightly curved outer section ensures a closing of the suction opening in the proximity of the maximum chamber volume. By means of the more heavily curved section, being arranged between two slightly curved sections, also the backflow is reduced. Thus, an improvement of the closing behaviour of the suction opening is achieved.
Further, it is advantageous that the first and the second sections each have a length of approximately xcfx80/3 in the arc measure. Through these relatively short outer sections, the chamber portion, through which a backflow can occur, is kept relatively small. In this way, the backflow can be reduced.
It is favourable that the profile back has a larger curvature on the outer limiting face than on the inner limiting face. In this way it is possible that, during a cycle of the scroll compressor, a contact point on the outer side of the profile back moves in another track than a contact point on the inner side of the profile back. Thus, an improved adaptation of different chambers in different phases to a predetermined volume function is possible.
It is advantageous that over a predetermined circulation length the profile back of one of the displacement elements on the inner limiting face has a contact point with an inner end of the other displacement element. This enables the stable creation of a chamber inside the scroll compressor.
Further, it is advantageous that in the cross section at least one of the displacement elements has at least two part elements, which are unmovable in relation to each other. This makes it possible to increase the number of chambers in a scroll compressor. In this way, the compression processes in different stages can take place in parallel within the scroll compressor. This improves the running smoothness of the compressor operation.
Further, it is advantageous that at least two of the part elements are connected with each other. Thus, a good mutual timing of the compression processes in different chambers can be ensured.